Enhanced proppant transport for hydraulic fracturing

ABSTRACT

The present disclosure relates to compositions and methods for recovery of hydrocarbons from subterranean formations. The compositions may be dry blends of synthetic and naturally derived polymers. The blend compositions may also be produced as high activity solvent-based fluidized polymer suspensions. Either in dry or liquid forms, the blend compositions provide higher proppant carrying capacity in comparison to conventional solutions, as well as improved breakability and crosslinking capacity.

BACKGROUND OF THE INVENTION Field of the Invention

This application relates generally to compositions and methods forrecovery of hydrocarbons from subterranean formations.

Description of Related Art

Hydraulic fracturing techniques are widely used to stimulate oil and gasproduction from low permeability reservoirs. During hydraulicfracturing, a fluid is injected into a wellbore under high pressurecausing fractures to open around the wellbore and into the subterraneanformation. Often a proppant, such as sand, is included in the fracturingfluid to keep the fractures open when the treatment is complete.Ideally, hydraulic fracturing creates high conductivity communicationwith a large area of the formation allowing for an increased rate of oilor gas production.

Slickwater fracturing is a type of hydraulic fracturing that uses a lowviscosity aqueous fluid to induce the subterranean fracture. Slickwaterfluids are basically fresh water or brine having sufficient frictionreducing agent to minimize the tubular friction pressures. Such fluids,generally, have viscosities only slightly higher than unadulteratedfresh water or brine. Typically, the friction reduction agents presentin slickwater do not increase the viscosity of the fracturing fluid bymore than one to two centipoise (cP).

Slickwater fluids often contain proppants. In light of the low viscosityof the fluid, its proppant-carrying capacity is lower than that of thecrosslinked polymer gels used for non-slickwater fracturing. A lowerconcentration of proppant requires a higher volume of fracturing fluidto place a sufficient amount of the proppant into the induced fractures.Proppant settling from low viscosity fracturing fluids within thehorizontal section of the wellbore, the manifold lines, and the pump isalso a concern. Excessive proppant settling within a horizontal wellborecan necessitate cessation of fracturing treatments prior to placement ofthe desired volumes. The proppant may also settle in the manifold linesbefore it even reaches the wellhead. The proppant may even settle in thepump, damaging the pistons. This is particularly a problem when theproppant is composed of high compressive strength, such as ceramics.Typically settling occurs as a result of insufficient slurry flowvelocity and/or insufficient viscosity to suspend the proppant. In orderto mitigate settling issues, high pumping rates are employed toeffectively suspend the proppant for transport. However, high pumpingrates can result in higher than desirable pumping pressures andexcessive fracture height growth. Further, since manifolds havedifferent dimensions, mere modification of pump rate for the fluid inone area may not address the problem in another. Because of the largequantities of fracturing fluid needed, the high velocity of the fluidflow, and the irregularities of the subterranean formation, energy lossfrom friction can often prevent effective fracturing of the formation.

The flow of a fluid through a conduit induces frictional energy losses.The pressure of the liquid in the conduit decreases in the direction ofthe fluid flow. For a conduit with a fixed diameter, this drop inpressure increases with an increasing flow rate. The pressure decreasesignifies the loss of energy. Slickwater fracturing relies on high pumprates typically above 100 bpm (barrels per minute); hence a large amountof energy is lost due to the friction between the conduit and fracturingfluid.

In rheology, the Reynolds number is a dimensionless ratio of theinertial forces to the viscous forces of a fluid under flow conditions.The Reynolds number can be used to characterize the fluid flow aslaminar or turbulent. Laminar flow occurs when the viscous forcesdominate the inertial forces resulting in a low Reynolds number.Turbulent flow occurs when the inertial forces dominate the viscousforces resulting in a high Reynolds number. Laminar flow occurs when thefluid flows in parallel sheets or coaxial layers with little mixingbetween the layers. Turbulent flow is the opposite of laminar flow andoccurs when there are cross-currents perpendicular to the flow of thefluid giving rise to lateral mixing and eddies.

Generally, high molecular weight linear polymers are used to alter therheological properties of the fluid so that the turbulent flow isminimized, thereby preventing consequent energy loss in the fluid as itis pumped through the pipe. A good friction reducer will cause a largedecrease in friction at small concentrations, will be inexpensive, willbe environmentally friendly, and will have high shear, temperature andpressure stability.

The most common friction reducers are polyacrylamide (PAM) polymers,available as emulsions or in granular forms. Various copolymers havealso been developed to further enhance the performance of apolyacrylamide friction reducer. Sodium acrylamido-2-methylpropanesulfonate (sodium AMPS) and acrylic acid are common monomers besides theacrylamide in these copolymers to improve the hydration of the frictionreducers.

Often there is difficulty in handling such high molecular weightdry/granular polymers because of their low rate of hydration and highviscosity when made into a stock solution. To circumvent these problems,the polyacrylamide-based polymer is often made as an emulsion, where thepolymer is dispersed in a hydrocarbon solvent, such as mineral oil, andstabilized with surfactants. Hydraulic fracturing fluids may contain theaforementioned polyacrylamide-based polymer emulsions and can alsocontain polymeric viscosifiers such as guar gum added separately asdisclosed in U.S. Pat. Nos. 3,658,734; 4,374,216; 4,425,241; 7,857,055;8,043,999; 8,044,000 and in U.S. Patent Publication No. 2014/0158355.

Another approach is to use dry pre-mixtures of additives which are thenconverted into a liquid just before injection into the wellbore.Examples include use of a dry blend of a polymer such as guar andadditives disclosed in U.S. Patent Publication No. 2006/0058198; and useof dry polyacrylamide for drilling fluid compositions disclosed in U.S.Pat. No. 7,351,680; U.S. Patent Publication No. 2012/0157356 and U.S.Patent Publication No. 2014/0121134.

Hydraulic fracturing has been a boon to the oil and gas industry. Manyoil and gas wells have been made more productive due to the procedure.However, the hydraulic fracturing business is now facing increasedscrutiny and governmental regulation. The industry is responding bysearching for more effective chemicals to put into their hydraulicfracturing fluids.

In addition, large volumes of water are required for hydraulicfracturing operations. Fresh water may be a limiting factor in someareas. A slickwater fracturing composition that can use a variety ofwater sources, such as produced water from the formation or flowbackwater after a well treatment, could significantly enhance the fieldapplicability.

There is an ongoing need to develop slickwater fracturing fluids thathave even more effective friction reduction to minimize the energy lossbut yet have sufficient viscosity for proppant-carrying capacity whilebeing safe and environmentally friendly.

BRIEF SUMMARY OF THE INVENTION

The present invention is related to a dry blend composition of syntheticand naturally derived polymers for use in hydraulic fracturing,particularly in slickwater fluids. The blend composition can also bemade available as a high activity solvent based fluidized polymersuspension. Either in dry or liquid forms, the blend composition thereofprovides higher proppant carrying capacity in comparison to conventionalsolutions, as well as improved breakability and crosslinking capacity.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a graph comparing polymer shear sweeps for suspensions 1-3 andcontrol 3 at atmospheric pressure and temperature ranging from ambientto 180° F.

FIG. 2 is a graph comparing friction reduction for suspensions 1 and 3,control 1 and guar in tap water.

FIG. 3 is a graph comparing crosslinked viscosity for suspension 1,control 1 and control 3 at ambient temperature.

DETAILED DESCRIPTION OF THE INVENTION

The fracturing fluid may contain one or more types of proppant. Suitableproppants include those conventionally known in the art includingquartz, sand grains, glass beads, aluminum pellets, ceramics, resincoated ceramics, plastic beads, nylon beads or pellets, resin coatedsands, sintered bauxite and resin-coated sintered bauxite.

The composition of the present invention includes at least onenaturally-derived polymer. Naturally-derived polymers occur in natureand can be extracted or chemically modified to improve functionality.They are often water-based polysaccharides. In one embodiment, thenaturally derived polymer may be cellulose or starch, or guar andderivatives thereof. In one embodiment, the naturally derived polymer isa guar source. In accordance with the principles of the invention, theguar source may include any grade of guar gum. In an aspect, the guarsource may be guar pod harvested from the endosperm of leguminous seeds.Typically the guar source may be the endosperm, also called the guarsplit, which constitutes approximately 30-40% of the seed. The guarsource may further be derived from the remainder of the seed, referredto as the hull (approximately 15%) and the inner germ (approximately45%). For instance, the guar source may be the refined guar split, whichis the polished fibrous layers that are removed from the husk. The guarsource may further be guar gum that is produced from refined guar splitby softening, flaking, pulverizing and sieving.

In an aspect, guar is in a powder form. Typically, powders having a sizeof between about 60 mesh and about 400 mesh, more typically betweenabout 100 to 325 mesh. The guar may have a particle size below 500 μm(micron), preferably below 300 μm and most preferably below 200 μm.

Suitable guar derivatives include carboxyalkyl guars and hydroxyalkylguars. Preferred are carboxymethyl guar, hydroxypropyl guar,hydroxyethyl guar, hydroxybutyl guar and carboxymethylhydryoxypropylguar. Preferably the hydroxyalkylated guar has a molecular weight ofabout 1 to about 3 million. In an aspect, the degree of substitution ofthe carboxylated guar is typically between from about 0.08 to about0.18. In an aspect, hydroxypropyl content of the hydroxyalkylated guaris typically between from about 0.2 to about 0.6.

The carboxyalkyl guar can be obtained in many ways, including a) usingpremium grade guar as the starting material to which the anionic groupsare chemically added; and/or b) selecting processing parameters thatprovide better uniformity in placing the anionic substituent on the guarpolymer backbone; and/or c) additional processing steps, includingultrawashing to remove impurities and refine the polymer. Preferredpolymers include those guars having randomly distributed carboxymethylgroups.

Guar derivatives may also be suitable for the dry compositions of thepresent invention. In an embodiment, guar may be chemically modified toproduce guar derivatives such as hydroxypropyl guar, carboxymethyl guar,carboxymethyl Hydroxypropyl guar and cationic guar.

Naturally-derived cellulosic derivatives suitable for use includecarboxymethyl cellulose, hydroxyethyl cellulose and carboxymethylhydroxyethyl cellulose; while naturally-derived starch derivativessuitable for use include carboxymethyl starch and hydroxyethyl starch.

Without limitation, useful polysaccharides for the practice of thisinvention may have average molecular weights typically in the range offrom about 200,000 to about 3,000,000.

In another aspect, the preferred guar, guar derivatives and cellulosederivatives have a solution viscosity of at least 3,500 cP (centipoise);preferably from about 4,000 to about 5,000 cP and most preferably higherthan 5,000 cP at 1%.

The composition of the present invention includes at least one syntheticfriction reducer. The synthetic friction reducer may be awater-dispersable acrylamide polymer or polyethylene oxide. It has beendiscovered that the acrylamide polymer enhances a fluid's hightemperature endurance. The acrylamide polymer may be a homopolymer or acopolymer of acrylamide monomers with one or more different monomers. Asused herein, the term homopolymer is meant to encompass polymers havingless than about 0.1% by weight of any other monomers. The acrylamidehomopolymer is a non-ionic polymer made of acrylamide monomers. Withrespect to the acrylamide copolymers, the other non-acrylamide monomersmay be selected to provide the acrylamide polymer ionic properties. Forexample, in the acrylamide-acrylate copolymer, the acrylate segments areanionic. Examples of suitable non-acrylamide monomers include acrylatemonomers, such as sodium acrylate, potassium acrylate and ammoniumacrylate. Examples of acrylamide copolymers also include acrylamidomethylpropane sulfonate (AMPS)-acrylamide copolymer. The copolymers maybe block or random copolymers. The non-acrylamide monomers may makeupfrom about 0.1% to up to about 50% or more of the copolymer, moreparticularly from about 5% to about 15%. Acrylamide-acrylate copolymersmay also be formed by hydrolysis of an acrylamide homopolymer typicallyconducted with heat under alkaline reaction conditions. As used herein,the expression “polyacrylamide” or “acrylamide polymer” are meant toinclude both acrylamide homopolymers and copolymers of acrylamide withother monomers unless stated otherwise or as is apparent from thecontext.

The polyacrylamide may have a weight average molecular weight of fromgreater than about 2 million; preferably greater than about 5 million;and more preferably greater than about 15 million. The polyacrylamidemay be used in the fluids of the invention in an amount of from about0.1% to about 5% by weight of the fluid. In certain applications, thepolyacrylamide may be used in an amount of from about 0.03% to about0.4% by weight of the fluid. The polyacrylamide may be added in liquidform, such as dispersed in mineral oil, glycol, water, or other carrier.The polyacrylamide may also be added in solid or particulate form.

In an embodiment, the synthetic friction reducer is polyethylene oxide.Polyethylene oxide (PEO) is a straight-chained, high molecular weightpolymer. The weight average molecular weight of the polyethylene oxideis between from about 1 million to about 20 million, more preferablybetween from about 2 million to about 10 million. Typically the amountof PEO in the fracturing fluid is between from about 10 ppm to about 400ppm, more typically between from about 20 ppm to about 100 ppm.

Typically the weight ratio of naturally-derived polymer to syntheticfriction reducer in the dry composition is between from about 3:1 toabout 1:3; more typically between from about 2:1 to about 1:1.

Previous attempts to combine guar or guar slurry with standardpolyacrylamide emulsions have not produced satisfying results.Conventionally, the guar polymer would hydrate in the emulsion packageof polyacrylamide and form a pasty mixture; or attempts to blend guarpowder with standard granular polyacrylamide friction reducer wereunsuccessful because the particle size and density difference betweenthe naturally derived polymer and synthetic friction reducer did notproduce a homogeneous blend. Instead, separation of the componentsoccurred.

By contrast, it has been discovered that when polyacrylamide is groundto a given particle size distribution, below 500 μm, preferably below300 μm and most preferably below 200 μm; homogeneity issues areresolved. The dry composition of the present invention can be put intosuspension at very high solids content with no hydration issues.

One advantage of the composition is that it may be more easily storedand transported to a well site. In addition, preparation of thefracturing fluid is simplified, as the dry composition delivers twoconstituents in a single form, thereby reducing the number of additivestreams into a fracturing fluid. Furthermore, the number of operationson location is reduced due to the reduced number of streams. The drycomposition also provides a reduction in volume and weight of thetreatment as compared to additives in liquid form.

Another advantage of the dry composition is stability. It is not subjectto freezing, thereby facilitating use in colder climates. In addition,the concentration of the components in the dry composition will notchange due to evaporation of solvent, which is particularly beneficialfor oilfields in warmer climates.

Still another advantage of the dry composition is improved activity interms of crosslinkability, proppant loading, viscosity and breakability.Crosslinking activity, particularly for zirconium and titaniumcrosslinkers, has been shown to decrease with time in solution. The drycomposition of the present invention reduces the time that thecrosslinker is in solution prior to being combined with the twopolymers, thereby maintaining a higher and more consistent level ofactivity.

A cross-linking agent may be used with the fluids. The cross-linkingagents used include boron or Group IV transition metal compoundcross-linking agents. The cross-linking agent may include zirconium,titanium and hafnium cross-linking agents and combinations thereof andmay include organometallic compounds. In particular, boron,organo-zirconium and titanium crosslinking agents are useful. Thecross-linking agent may be included in the fluid in an amount of fromabout 0.1% to about 1.5% by weight of the fluid, more particularly fromabout 0.01% to about 1.5% by weight of the fluid, more particularly,from about 0.02% to about 0.3% by weight of the fluid.

The fracturing fluid may also contain other conventional additivescommon to the well service industry such as corrosion inhibitors,surfactants, demulsifying agents, scale inhibitors, asphalteneinhibitors, paraffin inhibitors, gas hydrate inhibitors, dispersants,oxygen scavengers, biocides and the like.

Suitable surfactants will act as surface active agents and function asemulsifiers, dispersants, foamers or defoamers. In some embodiments ofthe invention, the surfactant is an anionic surfactant. Examples ofsuitable anionic surfactants include, but are not limited to, anionicsurfactants such as alkyl carboxylates, alkyl ether carboxylates, alkylsulfates, alkyl ether sulfates, alkyl sulfonates, alpha olefinsulfonates, alkyl phosphates and alkyl ether phosphates. Examples ofsuitable anionic surfactants also include, but are not limited to,cationic surfactants such as alkyl amines, alkyl diamines, alkyl etheramines, alkyl quaternary ammonium, dialkyl quaternary ammonium and esterquarternary ammonium compounds. Examples of suitable ionic surfactantsalso include, but are not limited to, surfactants that are usuallyregarded as zwitterionic surfactants and in some cases as amphotericsurfactants such as alkyl betaines, alkyl amido betaines, alkylimidazolines, alkyl amine oxides and alkyl quarternary ammoniumcarboxylates.

The compositions of the present invention are suitable for use in freshwater, brackish water and hard brine environments.

Conventionally, proppant loading for slickwater treatment is only up to2 ppa (pounds of proppant added). However, with the present invention, aproppant loading of at least about 3 ppa can be achieved. In an aspect,the amount of proppant in the fracturing fluid may even be greater thanabout 4 ppa.

Moreover, in conventional slickwater treatments, the liquid suspensionmade from the dry composition of the present invention for treating thewellbore has a viscosity only up to about 12 cPs at 4 pptg (pounds perthousand gallons) polymer loading. With the composition of the presentinvention, viscosity of greater than about 13 cP can be obtained. In anaspect, viscosity greater than about 15 cP can be obtained. The increasein viscosity is desirable for providing higher carrying/suspendingcapacity. The higher the viscosity, the more proppant can be suspendedin the liquid, particularly under laminar flow conditions.

Example 1

It was discovered that stable high polymer active content suspensions inmineral oil could be prepared with combined polymers to delivermultifunctional properties. The suspension composition of this inventionconsists of benzene, toluene and xylene-free mineral oil, organophilicclay, surfactant and a combination of powdered guar gum andpolyacrylamide polymers. Table 1 provides the compositions of thesuspensions tested.

TABLE 1 Detailed Suspensions Composition Ingredients Suspension 1Suspension 2 Suspension 3 Mineral Oil 45.5 45.5 45.5 Organophilic clay 22 2 Surfactant 1 0.5 0.5 0.5 Surfactant 2 2 2 2 Dry fine powder 25 3037.5 Polyacrylamide Guar gum 25 20 12.5

The suspension examples were prepared with SHELLSOL D80 mineral oilavailable from Shell Chemicals; surfactant 1 (TDA-9, C-13 alcoholethoxylate available from Sasol); surfactant 2 (LUMISORB, a sorbitansesqueoleate available from Lambent Technologies): organophilic clay(CCOC 882, available from Imperial Group); dry polyacrylamide (FLOJETAN943VHV, available from SNF); and guar (35-45 cPs grade). Thesuspension is prepared by adding the organophilic clay into the oilwhile mixing, followed by addition of the surfactants. Then the polymerblend of guar and polyacrylamide is added to the mixture andhomogenized.

The hydration profile of the various suspensions was assessed by meansof “linear gel viscosity at 3 min mark after the polymer addition”,corresponding to the hydration of the polymer after mixing in a WARINGblender for 2.5 minutes at 1500 rpm and stabilization on a Grace 3600viscometer set at 300 rpm for 30 seconds. The evaluation was conductedin tap water at 4.0 gptg (gallons per thousand gallons) polymer andviscosity measured at 3 minute mark after the initial addition (0.5minutes following the 2.5 minutes of mixing). The hydration profiles areillustrated by the viscosity data in Table 2.

Example 2

For this evaluation, suspension examples representative of thecomposition of this invention were compared to commercially availablepolyacrylamide emulsions-based friction reducers.

Data in Table 2 indicates clearly that the suspensions of this inventionsynthesized as described in Example 1 provide much higher linear gelviscosity than conventional compositions. Controls 1-3 are anionicpolyacrylamide based friction reducers commercially available.Furthermore, the suspensions of this invention do not require anyparticular hydration equipment to achieve such high viscosities. Thehighest viscosity is achieved with a combination of 50/50 ofguar/polyacrylamide combination. Suspensions 1 and 3 were evaluated fortheir friction reduction capacity. Results in FIG. 2 also show that fasthydration and good friction reduction levels were achieved with lowerloadings (0.3 gptg) vs current solutions at 0.5 gptg. As expected, thelow loading (0.30 gptg) is causing an increase in shear out, thesuspension 1 is much better for both inversion/hydration rate and maxpercent of friction reduction.

TABLE 2 Comparative Linear Gel Viscosity Profile in Tapwater Suspen-Suspen- Suspen- Control Control Control Ingredients sion 1 sion 2 sion 31 2 3 3 min 17 16.4 14.7 11.9 9.2 10.1 apparent viscosity @ 511 s⁻¹, cP(4 gptg, 2.5 min hydration @ 1500 rpm)

Example 3a

The comparative samples were further tested for their crosslinkingcapacity. The gel solutions of Table 2 were crosslinked with 2 gptgBXL-411 instant and self-buffered boron crosslinker, available fromUnivar Inc.

The gels made with the suspensions 1-3 of this invention produced strongand lipping gel, while gels with controls 1-3 did not crosslink. Resultsin FIG. 3 show comparative crosslinked viscosities at ambienttemperature on Grace 5600 HPHT viscometer. It is clear that superiorcrosslinking capacity of suspension 1 in comparison to controls 1 and 3,conventional synthetic friction reducers. The controls did notcrosslink, while suspension 1 achieves initial viscosity of about 200cP, which remained above 100 cP after one hour. This indicates that thisinvention provides multiple functionalities that would allow enhancedproppant transport and placement.

Furthermore, after hydration, the gel solutions (4 pptg of suspensions1-3) were subject to API shear sweeps (method RP 39). After a baselineviscosity was observed for 10 minutes at ambient temperature, a shearsweep was performed, followed by raising the gel temperature to 90° F.,145° F., and 175° F., with shear sweeps performed once the testtemperature was reached. The resulting data (FIG. 1) indicate to whatdegree the fluids remained non-Newtonian as the temperature increased.Some thermal thinning of the fluid takes place, but it is important tohighlight the fact that all the three suspensions fully hydrate with noparticular hydration equipment or conditions.

Example 3b

Crosslinking capacity of the compositions was also tested under hightemperature conditions. A gel of suspension 1 was prepared as describedin Example 1, with a concentration of 25 pounds polymer blend/1000gallons fracturing fluid. These gels were then buffered to a pH of 9-10and cross-linked with a high pH buffer, surface and delayed boroncrosslinkers available from Univar (BES-y and BXL-411).

The fluid viscosity was then measured using a Grace 5600 HTHPviscometer. The temperature was ramped from ambient to 180° F. over aperiod of ten minutes. Shear was measured at 100/s with periodic API(American Petroleum Society) shear sweeps. The gel produced was a stronglipping gel with a consistent viscosity over 100 cP at 180° F. Controlfluids did not gel with the addition of buffer and cross-linker. APIshear sweeps indicated an average n′=0.55 and K′=2.72 (both showingstrong non-Newtonian behavior at high temperature). Control fluidsyielded n′>1 above 130° F. and K′<0.7. These results provided in Table 3below indicate increased proppant carrying capacity.

TABLE 3 High Temperature Crosslinking Capacity Coefficient Visc. Kv(lbf- Determi- K' (lbf- K'Slot Visc. at Visc. at at 170 Shear Cycle TimeTemp. s{circumflex over ( )}n/ nation s{circumflex over ( )}n/(lbf-s{circumflex over ( )}n/ 40 (1/s) 100 (1/s) (1/s) Ramp No. (min) (°F.) n' 100 ft²) (R {circumflex over ( )}2) 100 ft²) 100 ft²) cP cP cP 11 13.7 183 0.6252755 1.319125 0.836 1.2596   1.401232 186.36 135.57112.76 2 1 23.7 182 0.533543  2.658727 0.658 2.500145 2.86566  245.52160.13 125.02 3 1 33.7 180 0.54435   2.436904 0.743 2.294692 2.623631233.93 154.08 120.99 4 1 43.7 179 0.443515  3.951964 0.894 3.6749584.29097  263.75 158.39 117.9  5 1 53.7 179 0.730751  0.957225 0.6740.923426 1.004999 178.22 139.26 120.72 6 1 63.7 179 0.41797   3.8283640.82  3.549101 4.162276 232.83 136.59 100.3  lbf = pounds-force visc. =viscosity n = power law index K = consistency

Example 4

The yield point and plastic viscosity of the suspensions were alsotested. Comparative gels were made as described in Example 1, with threeblends of the inventive compositions (70/30, 65/35, 60/40 guar/frictionreducer) as well as conventional treatments of xanthan or guar gum.Xanthan is known for its capacity to suspend proppant and cuttings atvery low shear rate, as indicated by the yield point. Samples weretested for linear gel viscosity using a Fann 35-type viscometer atambient temperatures, at 300 and 600 rpm. These results provided inTable 4 below are useful in calculating fluid yield point and plasticviscosity. The yield point and plastic viscosity of the compositions wascalculated to be 6-8 pounds/100 feet and 6-7 cP, where guar alone orxanthan alone each gave 3-5 pounds/100 feet and 5-6 cP.

TABLE 4 Yield Points and Plastic Viscosity Plastic Yield 15 # Hydrations300 rpm 600 rpm Viscosity Point Guar Reading  7.8 cP  6.3 cP 5 cP 3lb/100 ft² Dial  8 13 Xanthan Reading 11.5 cP  8.3 cP 6 cP 5 lb/100 ft²Dial 11 17 FR Visc. (60/40) Reading 13.9 cP 10.3 cP 7 cP 7 lb/100 ft²Dial 14 21 FR Visc. (65/35) Reading 13.5 cP 10.0 cP 6 cP 8 lb/100 ft²Dial 14 20 FR Visc. (70/30) Reading 13.1 cP  9.8 cP 7 cP 6 lb/100 ft²Dial 13 20 FR Visc. = friction reducer viscosity

Example 5

The compositions' tolerance to salt was also measured. Comparativesamples were prepared as in Example 1, with the addition of a givenamount of various salts representative of oilfield conditions. Afterhydration, the fluid viscosity was measured at ambient temperature usinga Fann 35-type viscometer at 511/s. As provided in Table 5 below, theinventive compositions showed the highest tolerance to two of threebrines tested.

TABLE 5 Viscosity Differences visc., cP @ Percent 511/s 2000 mg/lDifference in Viscosity Fluid GPT tap water NaSO₄ 3.5% NaCl 1% CaCl₂ A3.0 12 −30% −57% −83% A 5.0 20 −35% −59% −87% A 3.0 5.4  0% −33% −59% A5.0 9.4 −11% −45% −66% 60/40 3.0 11.8 −14% −22% −47% 60/40 5.0 21.6  −9%−23% −46% Fluid A = conventional friction reducer GPT = gallon perthousand gallons

Example 6

The comparative crosslinked samples may be further evaluated for theirbreakability. To a gel solution, 0.75-2.0 gptg standard breaker (enzyme,acid or oxidizer) would be added. The viscosity reduction profile wouldbe followed over time. It is anticipated that the solution viscosity ofthe solutions prepared with suspensions 1 to 3 of the present inventionwould show a higher viscosity reduction ratio as compared to controls 1to 3.

Example 7

The comparative gel solutions (which may or may not be crosslinked) maybe further evaluated for the capacity to increase proppant carryingcapacity. The proppant carrying capacity may be assessed by means ofstatic settling of various amounts of proppant in various gel solutionsover a period of time and compared side by side with the incumbentcontrols. It is anticipated that gel solutions made with suspensions 1to 3 would exhibit lower proppant settling rates in comparison tocontrols 1 to 3. It is further anticipated that the gel solutions ofsuspensions 1 to 3 would tolerate and suspend higher proppant loading(3-4 ppa (pounds of proppant added)) in comparison to controls 1 to 3that are anticipated to be limited to no more than 2 ppa.

For the present invention, each numerical value should be read once asmodified by the term “about” (unless already expressly so modified), andthen read again as not so modified unless otherwise indicated incontext. Concentration ranges listed or described herein include any andevery concentration within the range, including the endpoints. Forexample, “a range of from 1 to 10” is to be read as indicating each andevery possible number along the continuum between about 1 and about 10.Thus, even if specific data points within the range, or even no datapoints within the range, are explicitly identified, it is to beunderstood that inventors appreciate and understand that all data pointswithin the range are considered to have been specified, and theinventors have disclosed and enabled the entire range and all pointswithin the range.

It is understood that modifications to the invention may be made asmight occur to one skilled in the field of the invention within thescope of the appended claims. All embodiments contemplated hereunderwhich achieve the objects of the invention have not been shown incompete detail. Other embodiments may be developed without departingfrom the spirit of the invention or from the scope of the appendedclaims. Although the present invention has been described with respectto specific details, it is not intended that such details should beregarded as limitations on the scope of the invention, except to theextent that they are included in the accompanying claims.

What is claimed is:
 1. A composition comprising: mineral oil, from10-90% by weight of polyacrylamide; and from 10-90% by weight of guar.2. The composition of claim 1, wherein the polyacrylamide is a drypowder.
 3. The composition of claim 2, wherein the dry powder has aparticle size below about 500 μm.
 4. The composition of claim 1, whereinthe guar has a particle size below about 500 μm.
 5. The composition ofclaim 1, wherein the composition comprises about 25% to about 75% byweight of the polyacrylamide.
 6. The composition of claim 1, wherein thecomposition comprises about 40% to about 70% by weight of thepolyacrylamide.
 7. The composition of claim 1, wherein the guarcomprises a minimum solution viscosity of about 3,500 cP at 1%.
 8. Thecomposition of claim 1, wherein the polyacrylamide has a weight averagemolecular weight of at least about 2,000,000.
 9. The composition ofclaim 1, further comprising a liquid carrier.
 10. The composition ofclaim 9, wherein the liquid carrier comprises a glycol.
 11. Thecomposition of claim 1, further comprising a friction reducer.
 12. Thecomposition of claim 11, wherein the friction reducer is a water-solublepolymer.
 13. The composition of claim 12, wherein the water-solublepolymer is selected from the group consisting of polyacrylamide,polyethylene oxide and any combination thereof.
 14. The composition ofclaim 9, further comprising a cross-linking agent.
 15. The compositionof claim 9, further comprising an organophilic clay.
 16. The compositionof claim 9, further comprising a surfactant.